Britain's Prime Minister David Cameron delivers a speech at the Aberdeen Exhibition and Conference Centre in Aberdeen, Scotland on September 15. Cameron appealed to Scots' emotions on his last visit to Scotland before this week's historic referendum by warning them on Monday that a vote to leave the UK would be irreversible. The referendum on Scottish independence will take place on September 18, when Scotland will vote whether or not to end the 307-year-old union with the rest of the UK. Reuters/Dylan Martinez